1. Field of Invention
Exemplary aspects of the present invention relate to an apparatus for image forming, and more particularly to an apparatus for toner image forming capable of effectively controlling an image forming condition of an image forming mechanism for an adjustment at a predetermined timing.
2. Description of the Related Art
In general, related art image forming apparatus such as a copying machine, a printer, a facsimile machine, etc., employing an electrophotographic method, is provided with an image forming engine which is made based on a state-of-the-art technology involving different engineering fields, such as mechanical, electrical, and even chemical art. In many cases, the image forming engine is susceptible to changes, such as wear and tear of constituent components, conditions of power supply, and environmental factors, such as temperature and humidity, and so forth.
Therefore, the related art image forming apparatus is commonly provided with various adjustable parameters and is capable of adjusting these parameters to determine an image forming condition suitable for the image forming engine. The parameters may include a charge potential of a photoconductor, a development bias, a strength of optical writing relative to the photoconductor, and/or a target value of a toner density in a developer.
Such a parameter adjustment is typically performed when the background image forming apparatus is energized with power, or when it performs an image forming operation a predetermined cumulative number of times in units of sheet.
One exemplary parameter adjustment may optically measure an amount of reflection light relative to a surface of a photoconductor by using an optical sensor in two cases; no toner image is formed on the photoconductor surface and a reference toner image is formed on the photoconductor surface. A comparison is made on resultant reflection light amounts in the two cases. The comparison result can lead to an instant analysis of a toner density of the reference toner image on the photoconductor surface. Specifically, this process determines a toner amount of the reference toner image deposited in a unit area on the photoconductor surface. The determined toner amount becomes primary information based on which the parameter adjustment can be conducted.
As such, an output of the optical sensor is critical in the parameter adjustment. However, the optical sensor generally takes a relatively long time period to make an amount of light emission stable. FIG. 1 illustrates typical changes in an amount of light emission from one exemplary optical sensor at an initial power-on time. As shown in FIG. 1, this optical sensor needs several tens of a μsecond to make the amount of output light reach a maximal level. The emission amount, however, is gradually decreased as an internal resistance is increased with an increase in internal temperature of the optical sensor, and is stabilized when the increase in the internal temperature reaches a level of a saturation. In other words, an accurate reflection ratio of the light reflected by the reference toner image can only be detected after the optical sensor emits light in a stabilized manner, resulting in an undesirably lengthy duration of the parameter adjustment.